The invention relates to a method for encapsulating an integrated semi-conductor circuit (die) comprising the following steps:
a) mounting the semi-conductor circuit onto the surface of a so-called lead frame,
b) attaching connecting wires between the contact surfaces of the semi-conductor circuit and selected parts of the lead frame (bonding operation),
c) by means of a mould producing a plastic housing which at least encapsulates the semi-conductor circuit, the support surface, the bonding wires and part of the lead frame.
Such a method is generally known and is applied on a wide scale for encapsulating integrated semi-conductor circuits. In general the created housing will encapsulate the semi-conductor circuit completely such that only the connecting pins, forming part of the so-called lead frame, are extending outside the housing whereby the semi-conductor circuit as such is therefore screened from outer influences as much as possible.
In contrast therewith the invention is especially directed to a method for obtaining an encapsulation around an integrated semi-conductor circuit which comprises opto-electronic components whereby the housing should have a cavity which gives an open connection between the outside world and the active area on the `die`. If this cavity should be closed, it should be closed with window, opaque for radiation. Within the meaning of the invention radiation is both radiation in the visible part of the spectrum as well as radiation infrared or ultraviolet part of the spectrum.
The U.S. Pat. No. 5,200,367 comprises on the one hand a description of so-called ceramic housings and comprises on the other a description of a plastic housing which could be used as a replacement for the ceramic housing. In both cases however the housing is embodied such that the integrated circuit at the side, where the radiation should impinge on the circuit, is open. This open section can be covered by a separate plate of glass or, in case the semi-conductor circuit does not comprise any light sensitive components, be covered by a plate of another material such as a metal plate.
It is known for the expert in this field that the use of ceramic housings will lead to increase of costs of the final electronic component. Ceramic housings are therefore almost exclusively used for components which have to fulfil high requirements.
The steps, which successively have to be carried out according to the method described in U.S. Pat. No. 5,200,367 to obtain the desired end result are in their sequence clearly different from the generally used sequence. As is indicated shortly in the first paragraph, it is known to install first of all the chip or die on a lead frame and to attach the bonding wires between the chip or die and selected parts of the lead frame. Thereafter this intermediate product is encapsulated using a mould. This last step does not have to be carried out in a direct sequence with the earlier steps and can be performed at another location.
According to U.S. Pat. No. 5,200,367 first of all the lead frame is positioned within the mould and a housing is formed which is open at the upper side. Thereafter, the chip is installed on the related not covered section of the lead frame followed by bonding the connecting wires between the chip and selected sections of the lead frame (which for that purpose are not encapsulated in the housing). Both mentioned processes have to be carried out in a cavity in the already made housing. Because of that the number of possibilities to attach the chip to the lead frame is restricted. Welding at higher temperatures for instance will certainly lead to housing damage. Also the presence of the housing as such may for a hindrance for applying the usual bonding machines for attaching the bonding wires.